Techniques are known for controlling the output power of an RF power amplifier. A power detector, or the receiver path of a transceiver incorporating the power amplifier, can be used to measure the power of the signal from the amplifier output which is to be transmitted and the output power measurement can be applied over a feedback loop to a control circuit. The control circuit can compare the measured output power, and its variation in time, with a desired value defined by a reference signal and correct the output power.
It is known for the control circuit to control the gain of the power amplifier by controlling its operating conditions. Instead of using the feedback to control the output power by controlling the power amplifier gain, it is also known for the control circuit to control the power of the signal to be amplified supplied to the input of the power amplifier, known as input power control mode (‘IPCM’), for example by controlling the amplitude of a signal from a voltage controlled oscillator and its modulation by the data to be transmitted.
Some widespread radio transmission standards, such as Global System for Mobile communications (‘GSM’), General Packet Radio Service (‘GPRS’), Enhanced Data rates for GSM Evolution (‘EDGE’), for example, define the radio transmissions to be discontinuous and to occur in bursts. These standards contain tight specifications on the transmitted power, which is to be a function of command signals received, and also on the variation of the transmitted power during the burst, notably during the initial ‘ramp-up’ period of each burst. These specifications are more difficult to meet while also minimising the power consumption of the transmitter and notably of the power amplifier.
US Patent Specification US 200510227644 describes an envelope tracking RF power amplifier in which an RF input voltage is sampled by an adaptive envelope signal processing circuit which provides for constant power amplifier gain across the input signal dynamic range.
US Patent Specification 200610084398 describes an RF power amplifier which predictively determines a voltage value to continuously control a voltage converter for minimizing supply voltage or current drain of the power amplifier.
US Patent Specification 200610114062 describes a bias circuit for an RF linear power amplifier which includes a self-adaptable circuit that dynamically modifies the quiescent current for an output stage amplifier by automatically tracking an RF signal input to the amplifier at power ranges above a certain power output threshold.